全文获取类型
收费全文 | 4044篇 |
免费 | 329篇 |
国内免费 | 159篇 |
专业分类
电工技术 | 189篇 |
综合类 | 72篇 |
化学工业 | 206篇 |
金属工艺 | 136篇 |
机械仪表 | 129篇 |
建筑科学 | 91篇 |
矿业工程 | 29篇 |
能源动力 | 57篇 |
轻工业 | 119篇 |
水利工程 | 96篇 |
石油天然气 | 80篇 |
武器工业 | 9篇 |
无线电 | 308篇 |
一般工业技术 | 217篇 |
冶金工业 | 2438篇 |
原子能技术 | 21篇 |
自动化技术 | 335篇 |
出版年
2024年 | 17篇 |
2023年 | 67篇 |
2022年 | 126篇 |
2021年 | 147篇 |
2020年 | 103篇 |
2019年 | 78篇 |
2018年 | 89篇 |
2017年 | 68篇 |
2016年 | 73篇 |
2015年 | 99篇 |
2014年 | 84篇 |
2013年 | 103篇 |
2012年 | 105篇 |
2011年 | 82篇 |
2010年 | 78篇 |
2009年 | 67篇 |
2008年 | 62篇 |
2007年 | 69篇 |
2006年 | 85篇 |
2005年 | 100篇 |
2004年 | 40篇 |
2003年 | 41篇 |
2002年 | 65篇 |
2001年 | 41篇 |
2000年 | 29篇 |
1999年 | 101篇 |
1998年 | 779篇 |
1997年 | 480篇 |
1996年 | 303篇 |
1995年 | 158篇 |
1994年 | 143篇 |
1993年 | 126篇 |
1992年 | 29篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 32篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 24篇 |
1978年 | 3篇 |
1977年 | 70篇 |
1976年 | 143篇 |
1975年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有4532条查询结果,搜索用时 31 毫秒
1.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions. 相似文献
2.
图像纹理增强过程中容易丢失平滑区域纹理细节,而分数阶微分增强虽然能够非线性保留平滑区域纹理细节,但对频率分辨率敏感。针对这个问题,提出一种基于小波变换的分数阶微分纹理增强算法,应用于平扫计算机断层扫描(CT)图像的肝脏肿瘤区域的纹理增强。首先,通过小波变换将图像感兴趣区分解成多个子带分量;其次,基于分数阶微分定义构造一个带补偿参数的分数阶微分掩膜;最后,使用该掩膜与每个高频子带分量进行卷积并利用小波逆变换重组图像感兴趣区。实验结果表明,该方法在使用较大分数阶次显著增强肿瘤区域的高频轮廓信息的同时,有效地保留了低频平滑的纹理细节:增强后的肝细胞癌区域与原区域相比,信息熵平均增加36.56%,平均梯度平均增加321.56%,平均绝对差值平均为9.287;增强后的肝血管瘤区域与原区域相比,信息熵平均增加48.77%,平均梯度平均增加511.26%,平均绝对差值平均为14.097。 相似文献
3.
4.
5.
BACKGROUND: The enterococci have become important nosocomial pathogens. They can cause multiple site infections and enterococcal bacteremia becomes more frequently associated with a high mortality rate. Previous studies of enterococcal bacteremia showed a variety of results. To establish the significance and importance of enterococci as nosocomial pathogens in this hospital, to characterize their clinical pictures and to search for the risk factors for mortality, this retrospective study was performed. METHODS: There were 208 cases of enterococcal bacteremia which occurred from 1988 to 1992. Twenty-seven cases had no medical charts, dismissing possibility of evaluation. Finally, 181 cases of enterococcal bacteremia were analysed. RESULTS: One hundred and eighteen episodes were nosocomial infections. Polymicrobial bacteremia occurred in 68.5% of the patients and the most common co-isolate was Pseudomonas aeruginosa. Those patients (78.5%) with underlying diseases and malignancies were the most common underlying problems. The portal of entry could be found in 69.6 percent of patients, with the gastrointestinal tract the most common sources. Antimicrobial susceptibility testing showed high gentamicin resistance rate (89.5%), and ampicillin still had about 80 percent sensitivity rate. The group who received specific antibiotic therapy for enterococcus showed lower mortality (36.4% versus 47.6%). Only one case had infective endocarditis. Forty-nine patients suffered from septic shock, the cause of 30 deaths. Totally 75 patients died during hospitalization. Besides sepsis, another major cause of death was their underlying diseases itself. CONCLUSIONS: Enterococci have no doubt become important nosocomial pathogens and enterococcal bacteremia were associated with high mortality, especially in elderly patients with underlying diseases such as malignancy or diabetes. When clinically dealing with sepsis from the gastrointestinal or biliary tract, especially when previous cephalosporins therapy showed no response, the possibility of enterococcal bacteremia should always be considered. 相似文献
6.
NF Saba JD Sweeney LC Penn JC Lawton RL Yankee CH Huang MS Schanfield 《Canadian Metallurgical Quarterly》1997,37(3):321-324
PURPOSE: We report a case of postoperative reparalysis in the recovery room, following nebulized epinephrine. The patient was pharmacologically reversed with edrophonium after paralysis with rocuronium. CLINICAL FINDINGS: A 12-yr-old girl developed postoperative reparalysis following the intraoperative administration of rocuronium. A total of 0.92 mg.kg-1 rocuronium was administered. After surgery, pharmacological reversal was achieved with 20 mg edrophonium with 0.15 mg atropine sulfate iv 35 min after the last administration of rocuronium. Muscular relaxation was monitored using an ulnar peripheral nerve stimulator (PNS). After reversal, a full train-of-four and sustained tetanus at 50 Hz were present. In the recovery room, following nebulized epinephrine, the patient became apneic. The patient was paralyzed and an ulnar PNS demonstrated only one faint twitch. The paralysis was reversed with 1.5 mg neostigmine with 0.3 mg glycopyrrolate. CONCLUSION: Postoperative reparalysis following rocuronium may be a cause of postoperative respiratory distress. The definitive diagnosis is made using PNS and observing the response to pharmacological reversal. Nebulized epinephrine may have a previously undescribed role in the development of postoperative reparalysis. 相似文献
7.
8.
9.
10.
Human immunodeficiency virus (HIV) infection of the thymus could have profound effects on development of the immune response, particularly in children. We and others have established that in addition to infecting and depleting CD4-bearing thymocytes, functional HIV proviruses are found in thymocytes lacking surface CD4 expression. Using in vitro thymocyte cultures, we show that neither HIV-mediated down regulation of CD4 nor CD4-independent infection contributes to the localization of HIV in cells lacking the primary virus receptor. Rather, infection of a CD4-positive precursor cell (CD4 positive/CD8 positive) with subsequent differentiation into a mature CD4-negative phenotype results in productively infected CD4-negative cells. This novel mechanism may contribute to pathogenesis by distributing viral sequences into functional subsets of T cells typically refractory to HIV infection and could account for the presence of viral DNA in CD8-positive lymphocytes recently observed in patients. 相似文献